The third preseason game is usually treated as a dress rehearsal for the regular season, but the flux on the offensive line caused the Cowboys to call an audible.

Frederick was diagnosed last week with Guillain-Barre Syndrome, an autoimmune disease that affects the nervous system, and is likely to miss multiple weeks of the regular season. Smith (hamstring) and Martin (knee) are expected to be ready for the Sept. 9 season opener. Right tackle La’el Collins missed practice time during the week with an ankle injury and an illness, but he could see some action.

The Cowboys close the preseason Thursday at the Houston Texans and traditionally have not played any of their starters in the final game under coach Jason Garrett.

Elliott played in the first preseason game in each of his first two seasons, carrying seven times for 48 yards in 2016 and six times for 18 yards in 2017.

Prescott played 39 snaps in the Cowboys’ first two preseason games, completing 13 of 18 passes for 125 yards and two touchdowns with no interceptions.

The Cowboys also will be mindful of the work they give their defensive starters, including linebacker Sean Lee, who will not play, according to sources. Lee played in 10 snaps last week against the Cincinnati Bengals. The Cowboys also will monitor the work of defensive end DeMarcus Lawrence, but he should see some action.